【作者】 任伟；

【导师】 周林；

【作者基本信息】 重庆大学 ， 电气工程， 2015， 硕士

【摘要】 日益增大的光伏并网容量和光伏发电比重可能会对电力系统的低频振荡特性产生不良影响,大型光伏电站应该具备参与抑制电力系统低频振荡的能力。本文以大型光伏电站并入单机无穷大系统为研究对象,在建立应用于低频振荡分析的系统模型基础上,研究分析大型光伏电站对电力系统低频振荡特性的影响,进而提出大型光伏电站参与抑制电力系统低频振荡的控制策略。主要研究内容包括:(1)在考虑光伏电池输出特性、最大功率跟踪(MPPT)动态特性以及功率控制特性基础上分别建立了基于单位功率因数PQ模式、基于比例控制PV模式以及基于比例积分控制PV模式并网的大型光伏电站模型,同时结合同步发电机模型、PSS模型、输电线Π形等值电路最终建立应用于低频振荡分析的大型光伏电站并入单机无穷大系统数学模型。(2)基于特征根分析方法,以含PSS同步发电机+不含PSS同步发电机系统为参照对象,分别研究大型光伏电站替代不含PSS的同步发电机、大型光伏电站替代含PSS的同步发电机、大型光伏电站改变系统潮流分布以及大型光伏电站不同并网控制特性对电力系统低频振荡特性的影响。理论分析与仿真验证结果表明:大型光伏电站替代不含PSS的同步发电机将会减小系统低频振荡的阻尼,大型光伏电站替代含PSS的同步发电机将会显著减少系统低频振荡的阻尼;大型光伏电站并网容量增大、输电距离延长以及公共连接点位置越靠近同步发电机时均会减少系统低频振荡模式的阻尼,大型光伏电站采用基于比例积分控制PV模式并网比基于比例控制PV模式和基于单位功率因数PQ模式并网具有更大的低频振荡阻尼。本文进一步指出:在某些条件下,大型光伏并网系统存在低频振荡失稳解列的风险,大型光伏电站有必要采用合适的控制策略参与抑制电力系统低频振荡。(3)在分析电力系统低频振荡特性的基础上,参考PSS类控制器设计大型光伏电站抑制电力系统低频振荡的控制策略:提出采用广域输电线路有功微分信号调节大型光伏电站最大有功输出的自适应阻尼控制策略,该控制策略能够尽可能多的输出有功并且确保光伏电站低频振荡抑制模式与最大功率跟踪模式之间的平滑切换。同时,考虑到相关标准对无功调压能力的要求,大型光伏电站无功控制采用现有光伏系统无功调压的控制方法,进而形成大型光伏电站的功率控制策略。理论分析和仿真结果验证大型光伏电站有功阻尼控制策略能够显著提高系统抑制低频振荡的能力,保障系统安全稳定运行。更多还原

【Abstract】 With the growing of photovoltaic capacity and permeability, which is likely to be a harmful effect on the low-frequency oscillations of the power system, large-scale photovoltaic plants should have the ability to participate in restraining low-frequency oscillations. With the research object of single-machine infinite bus system including large-scale photovoltaic plants and based on establishing the system model which is used to analyze the low-frequency oscillations, this dissertation researches on large-scale photovoltaic plants impact on low-frequency oscillations of the power system, and proposing the control strategy to restrain low-frequency oscillations of the power system by large-scale photovoltaic plants. The main research contents include the the following parts:(1) Considering the dynamic behaviour of the photovoltaic battery output, maximum power tracking(MPPT) and power control, this dissertation establishes the large-scale photovoltaic plants model of PQ mode based on unit power factor, PV mode based on the P control and PV mode based on the PI control. Further more, combining with the model of synchronous generator, PSS, Π equivalent circuit of transmission line, the dissertation finally establishes the model of single-machine infinite bus system including large-scale photovoltaic plants which is used to analyze the low-frequency oscillations.(2) Based on the method of eignvalues analysis, and with the reference object of two synchronous generators that one has a PSS and the another has none, this dissertation researches on large-scale photovoltaic plants impact on low-frequency oscillations when the large-scale photovoltaic plants replaces the synchronous generator which include no PSS, when the large-scale photovoltaic plants replaces the synchronous generator which include a PSS, when the large-scale photovoltaic plants changes the power flow and when the large-scale photovoltaic plants adopts different control strategies. Theoretical analysis and simulation results show that: the large-scale photovoltaic plants replaces the synchronous generator which include no PSS will reduce the damping of low-frequency oscillations, the large-scale photovoltaic plants replaces the synchronous generator which include a PSS will significantly reduce the damping of low-frequency oscillations, it will reduce the damping of low-frequency oscillations with the increasing of the photovoltaic capacity, prolonging of the transmission line, closing to the synchronous generator of point of common coupling in the research system. the large-scale photovoltaic plants adopts the control strategy of PV mode based on the PI control provides more damping than the strategy of PQ mode based on unit power factor and PV mode based on the P control. The paper further points out that the large photovoltaic grid system carries the risk of leading to system instability under certain conditions, which is necessary for the large-scale photovoltaic plants to adopt appropriate control strategies to participate in restraining low-frequency oscillations.(3) Based on the analysis of characteristics of low-frequency oscillations, and refering to the PSS controller, this dissertation proposes the control strategy of restraining low-frequency oscillations by the large-scale photovoltaic plants. The adaptive damping control strategy using the differential signal of the active power on the wide-area transmission lines regulates the most active output in the large-scale photovoltaic plants. The strategy can offer active power as much as possible, and ensure smooth switching between low-frequency oscillation suppression mode and maximum power tracking mode. Considering the reactive power-voltage regulating ability in the related standards, the large-scale photovoltaic plants adopts the existing control strategy of power-voltage regulation. Theoretical analysis and simulation results show that: the large-scale photovoltaic plants which adopts the active damping control strategy can significantly improve the system’s ability in restraining low-frequency oscillations and guarantee the security and stability of the power system.更多还原